Project Summary Lichen planopilaris (LPP) is a subtype of primary cicatricial (scarring) alopecia caused by chronic lymphocytic inflammation centered around the hair follicle (HF) bulge stem cell region. The origin of LPP, like the other primary cicatricial alopecias (PCAs), remains poorly understood, however, they share the common finding of a targeted folliculocentric attack, which leads to irreversible HF destruction and permanent hair loss. LPP is a true dermatologic emergency, since delayed intervention will lead to irreversible, lifelong hair loss and permanent disfigurement of the scalp. Currently, few effective treatments are available for LPP, due to the lack of understanding of disease etiology and the difficulty of diagnosis among the subtypes of PCAs. Recently, one study of human LPP scalp skin implicated the collapse of immune privilege (IP) around HF epithelial stem cell niche during LPP pathogenesis, which was accompanied by the infiltration of cytotoxic CD8+ T lymphocytes that produce IFNgamma. This presentation is remarkably similar to another type of non-scarring inflammatory hair loss, alopecia areata (AA), in which the collapse of hair follicle IP results in the infiltration of inflammatory lymphocytes around the lower, bulb region of HFs, where it does not cause permanent scarring since the bulge stem cells are spared. Due to the striking similarities in both the collapse of HF immune privilege and the nature of the CD8+ T cell immune infiltrate in LPP and AA, we recently postulated that tofacitinib might also have efficacy in LPP, as we have shown in AA. Indeed, we recently treated 8 patients with LPP with tofacitinib, and observed a clinical response in about half of those treated. These exploratory studies have led to the initiation of a new Open-Label Pilot Study of Tofacitinib in Patients with LPP at Columbia University Medical Center, which will open in July 2017 and serves as the Parent Study for this application. In this Ancillary Study, we have the opportunity conduct a careful Immunophenotyping of LPP for the first time, directly from patient scalp and Tcells. We will identify pathogenic T cell populations, gene expression profiling from the skin and the blood, serum cytokine analysis, immunohistochemical definition of the Tcell infiltrate and high dimensional TCR sequencing. In line with the Parent Study, we will conduct subsequent immunomonitoring of LPP patient responses to tofacitinib during an open label clinical study. This Ancillary Studies project affords us the unique opportunity to conduct these critical immunophenotyping studies in LPP, which may have broader clinical relevance to other inflammatory and autoimmune diseases of the skin and hair follicle.